Currently, CT (Computed Tomography) scanners used in medical facilities can create cross-sectional images of a patient by the application of X-ray imaging. MRI (Magnetic Resonance Imaging) apparatuses can create cross-sectional images of a patient in real time with the magnetic resonance effect. Angiographic apparatuses can image blood vessels of a patient by the application of the X-ray imaging.
When the abovementioned apparatuses are used, a patient may be injected with a liquid such as a contrast medium and saline. Liquid injectors for automatically performing the injection have been put into practical use. Such a liquid injector has an injection head on which a syringe is removably mounted. The syringe has a cylinder member which is filled with a liquid. A piston member is slidably inserted into the cylinder member.
Some syringe products are already filled with liquids, and other syringe products allow operators to add desired liquids thereinto. When such a syringe is used in a liquid injector, the syringe is connected through a tank tube to a liquid tank filled with a liquid, and the syringe is mounted on an injection head, by way of example. The injection head separately holds a cylinder member and a piston member of the syringe and moves the piston member rearward from the cylinder member with a slider mechanism.
After the liquid is added into the syringe from the liquid tank, the liquid tank and the tank tube are removed from the syringe which, in turn, is connected to a patient through a patient tube. In this state, the injection heads moves the piston member forward into the cylinder member with the slider mechanism to inject the liquid from the syringe into the patient.
In the conventional liquid injector, however, an operator needs to connect the syringe to the liquid tank through the tank tube when the liquid is sucked from the liquid tank into the syringe, while the operator needs to remove the tank tube from the syringe and connect the patient tube to the syringe when the liquid is injected into the patient from the syringe. This requires complicated operation by the operator and thus raises the concern that the operator might contaminate the tank tube or patient tube.
To solve the abovementioned problem, another liquid injector has a syringe tube connected to a syringe, a tank tube connected to a liquid tank, and a patient tube connected to a patient, in which those tubes are connected through a switching valve. In the liquid injector, a liquid is sucked from the liquid tank into the syringe while the switching valve is manually operated to block the patient tube and connect the tank tube to the syringe tube.
Then, the liquid is injected into the patient from the syringe while the switching valve is manually operated to block the tank tube and connect the patient tube to the syringe tube. In such a liquid injector, since a liquid can be added into a small-capacity syringe from a large-capacity liquid tank, the liquid can be injected into a plurality of patients only by replacing the patient tube with another one.
In the abovementioned liquid injector, however, the operation is complicated since an operator needs to operate manually the switching valve. This may lead to erroneous operation, for example, the operator attempting to inject the liquid into the patient from the syringe while the patient tube is blocked and the tank tube is connected to the syringe tube, or the operator attempting to suck the liquid from the liquid tank into the syringe while the tank tube is blocked and the patient tube is connected to the syringe tube.
To solve the problem, the applicants have proposed a liquid injector which has a syringe tube connected to a syringe, a tank tube connected to a liquid tank, and a patient tube connected to a patient, in which those tubes are connected through a tube connecting means and a one-way valve is provided for each of the tank tube and the patient tube.
In the liquid injector, when an injection head moves a piston member rearward from a cylinder member, the one-way valve for the patient tube is closed and the one-way valve for the tank tube is opened, so that a liquid is sucked from the liquid tank into the syringe. On the other hand, when the injection head moves the piston member forward into the cylinder member, the one-way valve for the tank tube is closed and the one-way valve for the patient tube is opened, so that the liquid is injected into the patient from the liquid.
In the liquid injector, contamination can be prevented only by replacing the patient tube with another one for each patient, and a large amount of liquid in the liquid tank can be injected into patients through the syringe.
In reality, however, the one-way valve is formed in structure to be closed by a backflow of the liquid, so that a slight amount of blood or liquid may flow back into the syringe from the patient and then into the liquid tank from the syringe in the abovementioned liquid injector. In this case, the syringe and the liquid injector are contaminated, which means that the liquid cannot be injected into a plurality of patients even when a large-capacity liquid tank is used.